This invention relates to an ink jet printing apparatus for use with a facsimile machine, a copying machine, a printer, a computer output device, and the like.
A printing apparatus using an ink jet emission is disclosed in Japanese Unexamined Patent Publication No. 3-27949 in which ink is emitted from nozzles of a printing head to print an image or letter on a sheet of printing paper. Also, Japanese Unexamined Patent Publication No. 1-129667 discloses an image forming apparatus provided with an ink jet printing device.
The ink jet printing apparatus disclosed in Japanese Unexamined Patent Publication No. 3-27949 has a printing head in the form of a long bar which is secured to a main body of the apparatus and extends in a widthwise direction of the printing sheet. The printing sheet is fed in a lengthwise direction at a specified speed. Ink is emitted from the long printing head in synchronism with the lengthwise moving printing sheet to print a specified image on the printing sheet. This ink jet printing apparatus can print images at a high speed, but cannot print an image having a width larger than the long printing head.
Recently, also, there has been proposed an ink jet printing apparatus which enables printing of an image of A0-size. In the ink jet printing apparatus capable of printing a large-sized image, ink jet printing is executed as follows: A printing head having a specified size is reciprocally moved in widthwise direction of a sheet of printing paper. When being moved in a forward direction, the printing head emits ink onto the printing sheet in accordance with a control signal from a controller. In the forward movement, the printing sheet is held in a fixed position. When being moved in a reverse direction, the printing head emits no ink and the printing sheet is fed by a specified distance in a lengthwise direction of the printing sheet. These operations are repeated to print a specified image on the printing sheet.
However, the printing head of this ink jet printing apparatus is likely to suffer minute vibrations in the reciprocal movement and pressure fluctuations in an ink tube connected to the printing head, and consequently causes density variations in the printed image. To prevent such density variation, the printing head is forced to be moved within a limited speed. This has made it difficult to increase the printing speed of ink jet printing apparatus.